[johann28]

Enumeration like {X, Y, Z} is just one of the two main ways to define concepts. The other one is with a property, like {the Turing machines that halt on empty input}.

In the first case a meaningful question could be "what is the thing that makes these objects similar, what is a description that connects them?" For example if you see that certain animals die from some poison but others are unaffected. Then you may make up the concept of "resistastrong" animals that don't get killed.

You can do it in two very distinct ways. Either by enumeration, or by declaring the set as {the animals that don't die from the poison}. In the first case the definition is fixed and any more animals that are discovered to die from the poison are not accepted into the set. In the second case, the set may grow as more animals are discovered to die from the poison.

The way natural language works is often a hybrid of the two. We may call something a name, but then gradually the meaning can drift. We first have a fixed set. Then we realize some simple description that unites those things. Then we discover more things that fit this description and incorporate them in the set. Then we iterate again to find a better, more compact description of this new set. Maybe this will actually even throw out some of the elements that were previously included, because the description can be made much simpler if you throw out some edge case.